Multi-stage optical switching device

ABSTRACT

An optical switching device contains an active stage coupled to a passive stage. The index of refraction in the active stage is variable to change the entry direction of a light beam into the passive stage, which has a fixed index of refraction. Because the light beam can enter the passive stage at different angles, the exit direction of the light beam from the passive stage can be changed. The resulting optical switch allows switching without any mechanical components.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/715,181, filed Nov. 17, 2003, which is a continuation of U.S. patentapplication Ser. No. 10/373,974, filed Feb. 2, 2003, now abandoned,which is a continuation of U.S. patent application Ser. No. 10/027,096,filed Dec. 20, 2001, now U.S. Pat. No. 6,567,206.

TECHNICAL FIELD

The present invention relates to optical devices, and more particularlyto an optical device that refracts optical beams using electro-optic orphotorefractive materials.

BACKGROUND

Mechanical switches are used in many applications for controlling theoperation of a given device. Switches with mechanical moving parts arefamiliar and relatively simple, but suffer from problems common to allmechanical devices, including physical deterioration due to normal usage

There have been several proposed devices that switch light beams usingelectro-optic or photoreflective materials. Operation of one or moredevices may then be controlled by the changing direction of the lightbeams. Many of these devices use Kerr cells to change an index ofrefraction in the electro-optic or photorefractive material, but Kerrcells require high voltages to switch the beam direction. The highvoltages required make these types of switches impractical for consumerdevices

There is a need for a switchable or scannable optical device that doesnot experiences the shortcomings of currently known devices.

SUMMARY

Accordingly, the invention is directed to an optical device, comprisinga first element having a first index of refraction and a second elementthat communicates with the first element and has a second index ofrefraction, wherein one of said first and second elements can change theentry direction of a radiated beam into the other of said first andsecond elements.

The invention is also directed to an optical device, comprising anactive element having a first conductive substrate, a second conductivesubstrate, a first orienting layer; and a second orienting laterdisposed on the first and second conductive substrates and facing oneanother, and a refractive layer disposed between the first and secondorienting layers and having a variable index of refraction that isresponsive to the electric field. The optical device also includes apassive element, wherein the active element can change an entrydirection of a radiated beam into the passive element.

The invention is further directed to a method of manufacturing anoptical device, the method comprising providing an active element havinga refractive layer with a variable index of refraction between first andsecond conductive layers and coupling the active element to a passiveelement having a fixed or fixable index of refraction to form theoptical device, wherein a voltage applied to the first and secondconductive layers results in an electric field.

The invention is also directed to a method of manufacturing an opticaldevice, comprising providing a first element having a first index ofrefraction, providing a second element having a second index ofrefraction, and establishing communication between the first and secondelements.

Other embodiments, variations and advantages of the invention will beunderstood in view of the description below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a representative diagram illustrating one embodiment of theinventive optical device;

FIG. 2 is an edge view of the optical device shown in FIG. 1;

FIGS. 3 a and 3 b are representative diagrams illustrating an activeelement used in the embodiment shown in FIG. 1;

FIGS. 4 a through 4 c illustrate one method for manufacturing theinventive optical device; and

FIGS. 5 a and 5 b illustrate different reflected and refracted lightbeam paths based on changes in indexes of refraction.

DETAILED DESCRIPTION

FIG. 1 is a representative diagram of one embodiment of the inventiveoptical device 100, and FIG. 2 is a bottom view of the device in FIG. 1.Generally, the inventive optical device 100 changes the direction of anoptical beam from one position to another when a voltage is applied tothe device 100, allowing the beam to be selectably positioned, reflectedand/or transmitted. The optical device 100 in this embodiment includesan active element 102 and a passive element 104. The active element 102has a variable index of refraction, while the passive element 104 has afixed or fixable index of refraction. The passive element 104 may act asa total internal (TIR) stage, which will be explained in greater detailbelow.

FIGS. 3 a and 3 b are representative diagrams illustrating thecomponents in the active element 102. The active element 102 includestwo electrically conductive plates 300 facing each other with anorienting layer 302 deposited on each facing surface of the conductiveplates 300 and a refractive layer 304 sandwiched in between theorienting layers 302. Note that FIGS. 3 a and 3 b, as well as theremaining figures, are not drawn to scale and only illustrate therelative arrangement between different elements of the invention.

The electrically conductive plates 300 are substantially planar and canbe made of any conductive material. For example, the conductive plates300 can be made of metal. Alternatively, the conductive plates 300 canbe constructed by depositing an electrically-conductive material, suchas indium-tin-oxide, onto a glass plate, as illustrated in FIGS. 4 athrough 4 c and explained in greater detail below.

The orienting layers 302 are deposited onto the conductive plates 300and are generally used if liquid crystal molecules 306 constitutes therefractive layer 304. In one embodiment, the orienting layers 302 arethin vacuum deposited films of silicon monoxide, magnesium fluoride, orother material that can align the liquid crystal molecules 306 in therefractive layer 304. One possible way to deposit the films forming theorienting layers 302 is described in U.S. Pat. No. 3,834,792 to Janning,the disclosure of which is incorporated herein by reference in itsentirety. U.S. Pat. No. 3,834,792 teaches depositing the film at anoblique angle of around 85 degrees and at a thickness of approximately70 Angstroms. Other film structures can also be used in the orientinglayers 302 as long as the film structure can change liquid crystalmolecular alignment.

Of course, if the refractive layer 304 is constructed with a materialother than a liquid crystal layer, the orienting layer 302 structure andmaterial can be changed to be compatible with the refractive layer 304or omitted altogether. Possible refractive layer 304 materials includeliquid crystal molecules, as explained above, poly (N-vinylcarbazole)(PVK), PMMA or other photorefractive materials. Note that regardless ofthe specific material used for the refractive layer 304, the orientinglayer 302 can be omitted if the refractive layer 304 itself can beoriented for optimum performance.

The refractive layer 304 can be a material such as liquid crystalmolecules or another material whose index of refraction can change as asurrounding electric field changes. In this embodiment, the twoconductive plates 300 are separated by approximately 10 microns and havethe refractive layer 304 arranged between them.

As is known in the art, the liquid crystal molecules 306 are nematic, orcigar-shaped. In one embodiment, the liquid crystal molecules 306constitute the refractive layer 304 and are initially aligned in asubstantially heterotropic alignment, where the molecules 306 areparallel to the direction of the deposited thin film 302 and liesubstantially parallel to the conductive plates 300. This alignmentallows efficient operation of the optical device 100 by orienting theliquid crystal molecules 306 so that the initial index of refraction isat a minimum. FIG. 3 a illustrates one example where the input lightbeam 308 is parallel to the alignment angle of the liquid crystalmolecules in the refractive layer 304, allowing the output light beam310 from the active element 102 to go directly into the passive element.In one embodiment, the liquid crystal molecular alignment is selected toallow the maximum possible change in the index of refraction in therefractive layer 304.

Note that if the refractive layer 304 is composed of liquid crystalmolecules, then copper should not be used in the conductive plates 300because copper aligns the liquid crystal molecules 306 homeotropically(i.e., perpendicular to the conductive plate) rather thanheterotropically, interfering with the desired operation of theorienting layer 302.

With this active element 102 structure, applying a low voltage to theconductive plates 300 results in an electric field, causing the materialin the refractive layer 304 to change its index of refraction bychanging the arrangement of the liquid crystal molecules 306 as shown inFIG. 3 b. When the light beam 308 is directed through the refractivelayer 304, the change in the refractive layer's index of refractiondeflects the light beam's output path 310 from its original path by anamount dependent on the magnitude of the applied voltage and itscorresponding electric field.

FIG. 3 a shows the active element 102 when the refractive layer 304 isat its lowest index of refraction, while FIG. 3 b shows the activeelement 102 after an electric field changes the index of refraction inthe refractive layer 304. As shown in FIG. 3 a, before voltage isapplied to the conductive plates 300, the liquid crystal molecules 306are heterotropically aligned and are parallel to the conductive plates300. Because both orienting layers 302 are deposited in the samedirection in this embodiment, all of the liquid crystal molecules 306 inthe refractive layer 304 will lie in the same direction, keeping theindex of refraction at a minimum when no voltage is applied. In thiscase, the existing light beam 308 will travel through the refractivelayer 304 with its initial no-deflection orientation into the passiveelement 104. The actual minimum index of refraction is determined by theangle at which the input light beam enters the active element 102 andthe molecular alignment within the refractive layer.

When a voltage is applied to the conductive plates 300 to generate anelectric field, the liquid crystal molecules 306 will shift and alignthemselves parallel to the electric field when a high enough voltage isapplied, increasing the index of refraction of the refractive layer 304to its maximum value for the input light beams 308. As a result, theinput light beam 308 will be deflected from its original direction. Theoutput 310 will be at a different angle than its original no-deflectionorientation angle, and thereby enter the passive element 104 at adifferent angle. For example, if liquid crystal molecules are used forthe refractive layer, the index of refraction will be approximately 1.56in the absence of an electric field and 1.73 in the presence of asufficient electric field.

FIGS. 4 a through 4 c illustrates one manner in which the inventiveoptical device 100 can be manufactured and assembled using glass plates.In this embodiment, the active and passive elements 102, 104 are formedsimultaneously rather than as separate parts. More particularly, theembodiment shown in FIGS. 4 a through 4 c includes three glass plates400, 402, 404 that are layered together. The two outside glass plates400, 404 are approximately 1.1 mm thick and each have a layer ofindium-tin-oxide or other material 406 on a portion of the plate thatwill eventually become the active element 102. The indium-tin-oxidelayers 406 deposited on the glass plates 400, 404 act as the conductivelayers 300 in the active element 102, while the remaining, uncoatedportions 408 of the glass plates 400, 404 will form part of the passiveelement 104 in the finished device 100. If desired, the edges 410, 412of the two outside plates 400, 404 can have different profiles toprovide areas for electrical contact to the two outside plates 400, 404.

The third, middle glass plate 402 is sandwiched in between the twooutside plates 400, 404 and does not contact any portion of theindium-tin-oxide layers 406. The middle plate 402 is preferably thinnerthan the outside plates 400, 404, about 10 microns thick and acts as therefractive layer 304 of the passive element 104 and as a spacer betweenthe two outside plates 400, 404. The refractive layer material 414, suchas liquid crystal material, is placed in the space formed by the middleplate 402 to complete the active element 102. The middle plate 402 alsoacts as part of the passive element 100. Once the three layers 400, 402,404 are assembled together, a thin clear coating (not shown) can beapplied along the device's periphery to hold the layers together andcontain the materials in between the layers.

Note that the passive element 104 does not necessarily have to be anelement 402 having a fixed index of refraction. The passive element 104can also be an element 402 whose index of refraction can be varied aslong as the index is fixable at a predetermined value when used in theoptical device.

The passive element 104 acts as a total internal reflection (TIR) stageand the angle at which light exits the passive element 104 can becontrolled by changing the angle at which light enters the passiveelement 104.

Equations (1) through (5) below explain the relationships between theincidence angle at various interfaces in the optical device, therefracted angles in both the active and the passive elements, theminimum incidence angle needed for TIR, and the relationship between theindex of refraction in the passive and active elements 102, 104 andtheir corresponding refracted angles. The relationships of these anglesgiven by the equations are also a function of the geometric parameters αand β shown in FIGS. 5 a and 5 b. $\begin{matrix}{{r_{1}\left( {i,n_{1}} \right)} = {{arc}\quad{\sin\left( \frac{\sin(i)}{n_{1}} \right)}}} & (1)\end{matrix}$  i ₁(i,n ₁,α)=r ₁(i,n ₁)−α  (2) $\begin{matrix}{{r_{2}\left( {i,n_{1},n_{2},\alpha} \right)} = {{arc}\quad{\sin\left( {n_{1}\frac{\sin\left( {i_{1}\left( {i,n_{1},\alpha} \right)} \right.}{n_{2}}} \right.}}} & (3)\end{matrix}$ $\begin{matrix}{{r_{2}\left( {i,n_{1},n_{2},\alpha,\beta} \right)} = {\frac{\pi}{2} - \left( {\beta + {r_{2}\left( {i,n_{1},n_{2},\alpha} \right)}} \right)}} & (4)\end{matrix}$ $\begin{matrix}{{{TIR}\left( {n_{2},n_{exit}} \right)} = {{arc}\quad{\sin\left( \frac{n_{exit}}{n_{2}} \right)}}} & (5)\end{matrix}$where i=the incidence angle at the air/active-element interface

r₁=the refracted angle in medium 1 (the refractive layer 304 in theactive element 102 in this example) with a refractive index of n₁;

i₁=the incidence angle at the angled interface (in this example, theangled interface between the active element 102 and the passive element104);

r₂=the refracted angle in medium 2 (the passive element 104 in thisexample) with a refractive index of n₂;

i₂=the incidence angle at which the light beam strikes the interfacebetween medium 2 and the air;

TIR=the minimum incidence angle needed for total internal reflection inmedium 2;

n_(exit)=the refractive index of the exit material (in this example, theexit material is the ambient air, which has a refractive index of 1.0);

α=the angle formed by the interface between medium 1 and the air and theinterface between medium 1 and medium 2, as shown in FIGS. 5 a and 5 b;

β=the angle formed by the interface between medium 1 and medium 2 and avertical line, as shown in FIGS. 5 a and 5 b.

Note that the light beam in the passive element 104 can either exit thepassive element 104 or be reflected back into the passive element 104,depending on the incidence angle i₂. If i₂<TIR, then the light beam isonly slightly reflected back into the passive element 104, its angle ofrefraction rr₃ of the predominantly transmitted fraction is as follows:$\begin{matrix}{{{rr}_{3}\left( {i,n_{1},n_{2},\alpha,\beta,n_{exit}} \right)} = {{arc}\quad{\sin\left( {\frac{n_{2}}{n_{exit}}{\sin\left( {i_{2},\left( {i,n_{1},n_{2},\alpha,\beta} \right)} \right)}} \right)}}} & (6)\end{matrix}$

If, however, i₂≧TIR, then the light beam is totally reflected back intothe passive element 104, the angle of reflection r₃ is equal to i₂:r ₃(i,n ₁ ,n ₂,α,β)=i ₂(i,n ₁ ,n ₂,α,β)  (7)

As can be seen from Equations (6) and (7), if the incidence angle i₂ isequal to or greater than TIR, the light beam will be totally reflectedwithin the passive element 104 at an angle of reflection r₃ equal to i₂.Conversely, if the incidence angle i₂ is less than TIR, the light beamwill only be partially reflected back into the passive element 104 andinstead the major portion will exit the passive element 104 at arefractive angle of rr₃. In one embodiment of the invention, the lightat the interface between the active element 102 and the passive element104 is partially transmitted and partially reflected. The partialreflection is an undesirable, spurious signal whose magnitude attenuateseach time it is reflected. Increasing the length of the passive element104 increases the number of reflections, thereby reducing the magnitudeof the spurious signal to a more desirable level.

Thus, varying the index of refraction in the active element to changethe angle at which the light beam enters the passive element allows theinventive optical device to act as an optical switch by directing thelight beam to exit the passive element either through its side or itsend. For example, assume that the active element 102 is made usingliquid crystal molecules for the refractive material 304 and that thegeometric angles are set to α=50 degrees, and β=30 degrees. The examplealso assumes that the index of refraction n₂ in the passive element 104is n₂=1.46 and n_(exit)=1 (the refractive index of air). The index ofrefraction n₁ in the active element is swept between 1.56 and 1.73 toobtain the different light paths in this example. Thus, changing theindex of refraction n₁ of the active element 102 can change thedirection of the light ray as it enters the passive element 104. Forthese data, calculations using Equation (5) give the minimum incidenceangle, for TIR to occur, as 43.23 degrees. Further, assume that theincidence angle at the air-active element interface is i=52.3 degrees.In addition, if the active element 102 has its index of refraction setto 1.56, then the incidence angle i₂ at which the light beam strikes theinterface (between the passive element 104 and the ambient air) is 39.49degrees. In this case, the incidence angle is less than the minimumangle required for TIR, causing the light beam to refract at an angle ofrr3 and leave out the side of the passive element 104 rather than itsend.

By contrast, if the active element 102 has its index of refraction setto 1.73, the incidence angle is i₂, in the passive element 104, is43.299 degrees.

In this case, the incidence angle i₂ is greater than the minimum angleneeded for TIR. As a result, the light beam is totally reflected withinthe passive element 104 at a reflection angle of r₃=i₂ when it strikesthe interface between the air and the passive element 104 until itleaves through the end of the passive element 104.

FIGS. 5 a and 5 b illustrate the paths of multiple light rayscorresponding to multiple indices of refraction and reflection in theactive element 102. FIG. 5 a illustrates the results for the examplediscussed above. While FIG. 5 b presents results for a case where allthe light rays encounter total internal reflection in the passiveelement 104. In this example, it is assumed that i=40 degrees, while allthe other parameters are the same as in the previous example. The indexof refraction n₁ in the active element is swept between 1.56 and 1.73 toobtain the different light paths. Thus, changing the index of refractionn₁ of the active element 102 can change the direction of the light rayas it leaves the end of the passive element 104.

FIG. 5 a illustrates different exit paths that occur when the light rayis refracted out of the passive element 104 rather than reflected withinthe passive element 104. The example in FIG. 5 b assumes the samepassive and active element 102 characteristics as the example of FIG. 5a. The only difference between FIG. 5 a and FIG. 5 b is the incidenceangle i at which the light enters the active element 102: for FIG. 5 a,i=52.3 degrees, and for FIG. 5 b, i=40.0 degrees. For the example wherei=52.3°, the refracted light beam can be swept over an angular change ofover 20 degrees by varying the index of refraction n₁ in the activeelement 102 over a selected range, such as from 1.56 to 1.73. Further,as shown in this example, the optical device 100 can still achieve totalinternal reflection even with i=52.3 degrees if n₁ is set to 1.73.

Thus, changing the index of refraction in the active element 102 as wellas the incident angle i for the light beam as it enters the opticaldevice can direct the light beam either to exit out the side of theoptical device 100 or to reflect along the length of the passive element104 and exit out the end of the optical device 100. Further, changingthe index of refraction n₁ in the active element 102 can sweep or switchthe light beam direction at any selected time. As a result, theinventive optical device 100 can be used as a switch or scanner byplacing light-responsive elements in the refracted or reflected lightbeam's path. Adjusting the refractive index active element 102 can thenactivate and de-activate the light-responsive elements thereby directthe light beam toward or away from selected light-responsive elementsnear the optical device 100.

Although the examples described herein assume that a light beam entersthrough the active element into the passive element, the optical device100 can be adapted for any type of radiated beam. Further, the devicecomponents can be rearranged so that the radiated beam enters thepassive element first before being controlled by the active elementwithout departing from the scope of the invention. For example, theinvention may allow the passive element to change the entry direction ofthe radiated beam into the active element (rather than vice versa) toachieve total internal reflection.

Further, although the above description teaches an embodiment using anelectro-refractive material, whose index of refraction changes inresponse to a changing electric field, the inventive optical device canalso incorporate a photo-refractive material, whose index of refractionchanges in response to changes in illumination from a high-intensitylight source. Either material can be used in the active element toprovide a variable index of refraction.

The active element can also allow a light beam to scan over a given areaor device from one position to another without mechanically moving anyparts to conduct the scanning. The low operating voltage and thepossible small size of the inventive device allows the invention to beincorporated into virtually any device that normally uses a mechanicalswitch, including common consumer devices.

It should be understood that various alternatives to the embodiments ofthe invention described herein may be employed in practicing theinvention. It is intended that the following claims define the scope ofthe invention and that the method and apparatus within the scope ofthese claims and their equivalents be covered thereby.

1. An optical device, comprising: a first element having a first indexof refraction; a second element that communicates with the first elementand has a second index of refraction, and non-conductive plates at leastpartially overlaying the first and second elements, wherein one of saidfirst and second elements includes a portion having first and secondconductive layers or plates, that element can change the entry directionof a radiated beam into the other of said first and second elements, andthe radiated beam is substantially transmitted through the portionbetween the conductive layers or plates.
 2. The optical device of claim1, wherein the first element has a variable index of refraction and thesecond element has a fixed index of refraction.
 3. The optical device ofclaim 1, wherein the first element has a first variable index ofrefraction and the second element has a second variable index ofrefraction.
 4. The optical device of claim 3, wherein the secondvariable index of refraction is fixable to a selected value.
 5. Theoptical device of claim 1, wherein the first element can change theentry direction of a radiated beam into the second element.
 6. Theoptical device of claim 1, wherein the first element includes arefractive layer that is responsive to an electric field.
 7. The opticaldevice of claim 6 wherein the electric field is variable.
 8. The opticaldevice of claim 1, wherein the first element includes a refractive layerthat is responsive to at least one of a magnetic field andhigh-intensity light.
 9. The optical device of claim 1, wherein thefirst element includes a refractive layer that comprises at least oneselected from the group consisting of liquid crystal, poly(N-vinylcarbazole) (PVK), PMMA, or a photorefractive material.
 10. Theoptical device of claim 1, further comprising an adjustment mechanism incommunication with the first element to control a first variable indexof refraction.
 11. The optical device of claim 10, wherein theadjustment mechanism is a variable voltage source and wherein applying avariable voltage to the first and second conductive layers or platesresults in a variable electric field.
 12. The optical device of claim11, wherein the first and the second conductive layers or plates arecomprised of metal.
 13. The optical device of claim 11, wherein thefirst and second conductive layers or plates comprise an electricallyconductive material deposited on the non-conductive plates.
 14. Theoptical device of claim 1, wherein the optical device controls an exitdirection of the radiated beam to switch between a first direction and asecond direction.
 15. The optical device of claim 1, wherein the opticaldevice controls an exit direction of the radiated beam to scan over aselected range.
 16. A method of manufacturing an optical device, themethod comprising: providing an active element having a refractive layerhaving a variable index of refraction between a first conductive layerand a second conductive layer, the first and second conductive layersbeing comprised to substantially retain the transmission of a radiatedbeam therebetween; and coupling the active element to a passive elementwith non-conductive plates at least partially overlaying the active andpassive elements, wherein the passive element has a fixed or fixableindex of refraction, wherein a voltage applied to the first and secondconductive layers results in an electric field.
 17. The method of claim16, further comprising establishing communication between a variablevoltage source and the first and second conductive layers to vary theelectric field.
 18. The method of claim 16, further comprisingdepositing an active element conductive material on a portion of thenon-conductive plates to comprise at least a portion of the activeelement, wherein a portion of the non-conductive plates that does notreceive a deposit of an active element conductive material comprises thepassive element.
 19. A method of manufacturing an optical device,comprising: providing a first element having a first index ofrefraction; providing a second element having a second index ofrefraction; providing non-conductive outer plates that at leastpartially overlay the first and second elements; and establishingcommunication between the first and second elements, wherein at leastone of the first and second elements has a portion that includes firstand a second conductive layers or plates, and wherein the first andsecond conductive layers or plates substantially retain the transmissionof a radiated beam therebetween.
 20. The method of claim 19, wherein thefirst index of refraction is variable.
 21. The method of claim 19,wherein the second index of refraction is variable.
 22. The method ofclaim 21, wherein the second index of refraction is fixable.
 23. Themethod of claim 19, wherein the second index of refraction is fixed. 24.The method of claim 19 further comprising depositing an active elementconductive material on a portion of the non-conductive outer plates toform an active element portion and a passive element portion.
 25. Anoptical device, comprising: a passive element portion; an active elementportion that communicates with the passive element portion; andnon-conductive outer plates that at least partially overlay the activeand passive element portions, wherein the active element portionincludes a refractive portion between the non-conductive outer plates,wherein the passive element portion includes a non-conductive middleplate between the non-conductive outer plates.
 26. The optical device ofclaim 25, wherein said active element includes anelectrically-conductive material between the refractive portion and eachnon-conductive outer plate that can change the entry direction of aradiated beam directed to traverse the active and passive elements. 27.The optical device of claim 25, wherein the non-conductive outer platesand non-conductive middle plate each comprise glass.
 28. The opticaldevice of claim 26, wherein the electrically-conductive material isdeposited on an inner surface of each non-conductive outer plateadjacent the refractive portion.